Objective: To investigate if cone beam CT (CBCT) can be used to estimate the delivered dose in head and neck intensity-modulated radiotherapy (IMRT). Methods: 15 patients (10 without replan and 5 with replan) were identified retrospectively. Weekly CBCT was coregistered with original planning CT. Original high-dose clinical target volume (CTV1), low-dose CTV (CTV2), brainstem, spinal cord, parotids and external body contours were copied to each CBCT and modified to account for anatomical changes. Corresponding planning target volumes (PTVs) and planning organ-at-risk volumes were created. The original plan was applied and calculated using modified pertreatment volumes on the original CT. Percentage volumetric, cumulative (planned dose delivered prior to CBCT 1 adaptive dose delivered after CBCT) and actual delivered (summation of weekly adaptive doses) dosimetric differences between each per-treatment and original plan were calculated.Results: There was greater volumetric change in the parotids with an average weekly difference of between 24.1% and 227.0% compared with the CTVs/PTVs (21.8% to 25.0%). The average weekly cumulative dosimetric differences were as follows: CTV/PTV (range, 23.0% to 2.2%), ipsilateral parotid volume receiving $26 Gy (V26) (range, 0.5-3.2%) and contralateral V26 (range, 1.9-6.3%). In patients who required replan, the average volumetric reductions were greater: CTV1 (22.5%), CTV2 (26.9%), PTV1 (24.7%), PTV2 (211.5%), ipsilateral (210.4%) and contralateral parotids (212.1%), but did not result in significant dosimetric changes. Conclusion: The dosimetric changes during head and neck simultaneous integrated boost IMRT do not necessitate adaptive radiotherapy in most patients. Advances in knowledge: Our study shows that CBCT could be used for dose estimation during head and neck IMRT.Radiotherapy alone or chemoradiation is used in the primary treatment of head and neck squamous cell carcinomas (HNSCCs). Intensity-modulated radiotherapy (IMRT) allows dose conformality and organ-at-risk (OAR) avoidance in the complex head and neck anatomical region and is therefore the standard of care.